We have designed a fundamentally new instrument, which combines the capabilities of three instruments in a unique manner that overcomes the limitations of each instrument:
A) Spectrum Analyzers (SAs) provide absolute magnitude measurements over a wide bandwidth (e.g. 2-20 GHz) and can provide absolute phase relationship measurements over a small instantaneous bandwidth (e.g. approximately 50 MHz). SAs have the following advantages: high dynamic range (e.g. 150 dB), they can use narrow-band RF filtering for preselection to avoid spurious signals, and they can use preamplifiers for optimum noise figure. SAs have the following limitations: The instantaneous bandwidth over which phase can be measured may be much too small for current wide-bandwidth applications. In addition, the RF preselection filters can lead to unacceptable measurement errors (e.g. several dB and tens of degrees) in certain applications.
B) Vector Network Analyzers (VNAs) can provide relative S-parameter measurements over a wide bandwidth (e.g. 2-20 GHz). VNAs have the following advantages: relative vector error correction and high accuracy (0.1 dB and 1 degree). Conventional VNAs have the following limitations: There is no absolute phase relationship measurement between different frequencies. Also, there is no swept preselection filter to eliminate spurious signals.
C). Sampling oscilloscopes are used for absolute magnitude and absolute phase relationship measurements over wide bandwidths (e.g. 1 to 20 GHz). A serious limitation of sampling oscilloscopes is the limited dynamic range inherent in this technology (e.g. 20 to 40 dB with practical data-acquisition times). Several other related instruments, such as the Large Signal Network Analyzer, use a down-conversion circuit, which is based on the same principle as the sampling oscilloscope, and which have the same limited dynamic range.
The new Wideband Absolute VEctor Signal (WAVES) measurement system uses two receiver channels per measurement port, and provides absolute magnitude and absolute phase relationship measurements over wide bandwidths (e.g. approximately 2 GHz). Gain ranging is used at RF to provide optimum noise performance and a swept YIG preselector filter is used to avoid spurious signals. A new Absolute Vector Error Correction (AVEC) method is used to calibrate the WAVES measurement system in order to allow for absolute vector measurements and it also removes the time-varying responses caused by the swept YIG preselector filters. The WAVES measurement system, therefore, has all the advantages of both the SA and the VNA instruments, without any of the limitations.
A sampling oscilloscope and a quasi-reciprocal mixer with a characterized non-reciprocal ratio are used at RF to provide the absolute calibration standard for the WAVES measurement system. Since the sampling oscilloscope is used only with known, high signal-to-noise calibration signals, there are no problems with the limited dynamic range of the sampling scope.
The two receiver channels in the WAVES receiver can be adapted to a wide variety of applications, including wide bandwidth vector signal analyzer measurements, network analyzer measurements, mixer measurements, and harmonic measurements. The two-channels can also be used as an absolute calibrated transmitter/reflectometer.